(a) Technical Field
The present invention relates to a multilayer dash isolation pad having superior formability and sound absorption performance. The multilayer dash isolation pad may include a compressed felt that is manufactured using octalobal cross-section fibers having an increased specific surface area compared to regular fiber and having a shape factor of 2.0 to 2.7, thereby providing enhanced N.V.H (Noise, Vibration, Hashness) and formability without increase of the weight and thickness of a decoupler and a sound absorption and insulation layer.
(b) Background Art
Vehicle dash isolation pads are based on a spring-mass structure as a structure for maximizing sound transmission loss and basically includes a decoupler functioning as a spring function and a sound absorption and insulation layer functioning as mass as illustrated in FIG. 1.
Generally, a decoupler is manufactured from urethane foam or soft felt, and a sound absorption and insulation layer is made of either a heavy layer or a compressed felt manufactured from a thermoplastic resin such as TPE or EVA, or a composite lamination of a heavy layer and a compressed felt that has been known as ‘needle punched nonwoven fabric’ in the related arts. In some small vehicles, the soft felt is used instead of urethane foam for weight reduction of components.
Conventionally, the density and thickness of decouplers and sound absorption and insulation layers have been increased to enhance sound transmission loss performance of dash isolation pad. However, when a density is continuously increased in given constant volume, structures of a cell and a pore may become unstable, thereby decreasing sound absorption and damping performance. In addition, thickness increase of components is limited due to interference relation with other components, and increase of the densities and thicknesses of multilayer materials leads to weight increase of components, thereby causing decrease in vehicle fuel efficiency. Therefore, it is important to enhance sound transmission loss performance by optimizing materials constituting a multilayer pad.
In related arts, Korean Patent No. 10-2011-0034522 reports a sound absorption material using a modified cross-section fiber and a method of manufacturing the same. As illustrated in FIG. 2, the modified cross-section fiber is utilized to enhance sound absorption performance by increasing a surface area in which sound waves can be disappeared with respect to circular cross-section fiber.
However, since the technology is limited to a technology for a fiber cross-section shape and plate-type felt and the shape of the plate-type felt is simple, the plate-type felt may be suitable for construction materials that are cut into a predetermined size without a molding process.
However, since the felt should be molded into a complex three-dimensional shape through a cooling press after heating at a temperature of about 180 to 200° C. to use as a sound absorption material of vehicle components, problems in component formability such as felt contraction due to excessive heat and surface collapse of felt may occur when the felt is used. Further, due to such a contraction phenomenon, there is still a limitation such as decrease in efficiency of sound transmission loss performance.
In dash isolation pads, felt is not used alone and used as a composite through composite-lamination with a decoupler, a heavy layer, and the like. As such, poor formability problems such as felt thickness decrease, non-uniform felt surfaces and compression elasticity decrease may be caused due to different heat contraction percentages between different materials.
Therefore, there is a need for a dash isolation pad having superior sound absorption performance while addressing problems, for example, formability such as felt thickness change, non-uniform felt surfaces and compression elasticity decrease, due to different heat contraction percentages between different materials.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.